The present invention relates to an air throttle valve for controlling the air flowing through an internal combustion engine, such as a spark ignited or compression ignition internal combustion engine.
Throttle valves have been used with internal combustion engines for well over a century. Most commonly used throttle valves include a round or oval plate, usually made of brass or aluminum. The throttle plate extends through a slotted, or slab cut, rotatable shaft which passes through the walls of an air passage. Typically, the air passage may be incorporated in a device such as a throttle body for use within a fuel injected engine; alternatively, the air passage may be incorporated into the housing of a mixing device such as a carburetor. Throttle devices with oval plates rely upon a nearly line-on-line contact between the majority of the throttle blade periphery and the throttle housing to achieve a near-zero or low airflow condition corresponding to engine idle operation. However, to avoid sticking of the throttle plate it is necessary to maintain a clearance between the throttle plate and the bore within which the plate is housed. Unfortunately, it is very difficult to achieve a precise low flow condition with conventional valve geometry, because air leakage through the clearance regions causes widely varying airflow.
A throttle valve assembly according to present invention solves problems inherent with known throttle valves by providing a throttle plate having a spherical section which rides directly upon the throttle bore, so as to provide superior sealing of the throttle plate in the bore. Because the spherical section throttle plate has only a single defining dimension, the orientation issues arising with other plate geometries are avoided.